Anode active material for lithium secondary batteries

ABSTRACT

Disclosed are an anode active material for lithium secondary batteries, the anode active material comprising: a core part including a carbon-silicon complex and having a cavity therein; and a coated layer which is formed on the surface of the core part and includes a phosphor-based alloy.

CROSS-REFERENCE TO RELATED APPLICATION

This present application is a continuation in part application of U.S.patent application Ser. No. 14/267,189 filed on May 1, 2014, which is acontinuation of International Application No. PCT/KR2012/010582 filed onDec. 6, 2012, which claims priority under 35 USC 119(a) to Korean PatentApplication No. 10-2011-0129605 filed in the Republic of Korea on Dec.6, 2011 and Korean Patent Application No. 10-2012-0141426 filed in theRepublic of Korea on Dec. 6, 2012, the disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an anode active material for asecondary battery, and more particularly, to an anode active materialfor a secondary battery comprising a phosphorus-based alloy coatinglayer on a surface of a carbon-silicon composite.

BACKGROUND ART

Different types of electrolytes are widely being used in electrochemicaldevices, such as lithium secondary batteries, electrolytic condensers,electric double layer capacitors, electrochromic display devices, aswell as dye-sensitized solar cells of which various studies are beingconducted for future commercialization, and so the importance ofelectrolytes is growing day by day.

Particularly, lithium secondary batteries are attracting the mostattention due to their high energy density and long cycle life.Generally, a lithium secondary battery includes an anode made from acarbon material or a lithium metal alloy, a cathode made from lithiummetal oxide, and an electrolyte in which a lithium salt is dissolved inan organic solution.

Initially, lithium metal was used as an anode active material comprisingan anode of a lithium secondary battery. However, because lithium hasdrawbacks of low reversibility and safety, currently, carbon material ismainly used as an anode active material of a lithium secondary battery.A carbon material has a lower capacity than a lithium metal, but hasmerits of a small volume change, excellent reversibility, and a low costadvantage.

However, as the use of lithium secondary batteries are expanding, thedemand for high-capacity lithium secondary batteries is also increasing.Accordingly, there is a demand for high capacity anode active materialsthat may substitute the carbon material having low capacity. To meet thenecessity, attempts have been made to use, as an anode active material,a metal that exhibits a higher charge/discharge capacity than a carbonmaterial and allows electrochemical alloying with lithium, for example,Si, Sn, and the like.

However, this metal-based anode active material has a very great volumechange during charging and discharging, which may cause cracks to anactive material layer. Accordingly, secondary batteries using thismetal-based anode active material may suddenly deteriorate in capacityand reduce in cycle life over repeated cycles of charging/discharging,and thus are not suitable for commercial use.

To solve these problems, studies have been conducted to use an alloy ofSi and/or Sn and another metal as an anode active material. However,although the use of such an alloy contributes to the improvement ofcycle life characteristics and prevention of volume expansion to someextent when compared with the use of metal alone as an anode activematerial, the volume expansion generated during alloying with lithiumstill causes stress, thereby leading to an insufficient commercial useof secondary batteries.

DISCLOSURE Technical Problem

The present disclosure is designed to provide an anode active materialfor a lithium secondary battery using Si that may relieve stress causedby volume expansion generated during alloying with lithium.

Technical Solution

To achieve the above object, there is provided an anode active materialfor a lithium secondary battery, comprising a core including acarbon-silicon composite and having a cavity formed inside; and acoating layer formed on a surface of the core and including a phosphorus(P)-based alloy wherein the coating layer entirely covers the coresurface.

The coating layer may have a plurality of domains which are protrudedfrom the coating layer surface. In the present disclosure, the word‘domain’ means the parts of the coating layer which are protruded fromthe surface like embossed one and consist of and filled with the samematerial as the coating layer. Therefore, the domains include aphosphorus-based alloy. The phosphorus-based alloy may use an alloy ofphosphorous and a metal selected from the group consisting of Al, Ti,Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Pd, Ag, In, Sn, and W.

Also, the carbon-silicon composite may further include oxygen.

A density of the coating layer is preferably in a range of 1.2 to 5.8 gcm⁻³, and a thickness of the coating layer including domains ispreferably equal to or less than 0.1 μm.

A specific surface area of the core is preferably equal to or less than50 m²/g, and an average particle diameter of the core is preferably in arange of 0.5 to 100 μm.

Also, the anode active material of the present disclosure may be used inan anode of a lithium secondary battery comprising a current collector,and an anode active material layer formed on at least one surface of thecurrent collector and including an anode active material. Also, usingthis anode, a lithium secondary battery comprising a cathode, an anode,and a separator interposed between the cathode and the anode may beprovided.

A method of manufacturing the anode active material for the lithiumsecondary battery according to an embodiment of the present disclosurecomprises treating a silicon polymer particle with a metal chloridesolution to prepare the silicon polymer particle with a metal catalystsupported on a surface, dispersing the silicon polymer particle with themetal catalyst supported on the surface in a plating bath filled with aplating solution containing a metal ion for a phosphorous-based alloyand phosphoric acid, heating the bath to form a phosphorous (P)-basedalloy surface-coated silicon polymer particle, and carbonizing thephosphorous (P)-based alloy surface-coated silicon polymer particle byheat treatment in a reducing atmosphere.

The silicon polymer particle is not limited to a specific type, but mayuse a particle of silicon resin, for example, polysiloxane, polysilane,and polycarbosilane.

Also, the metal chloride solution may be one that metal chlorideselected from PdCl₂, SnCl₂, and CuCl₂ is dissolved in an aqueoussolution of nitrohydrochloric acid or hydrochloric acid, or in a polarorganic solvent of dimethylformamide (DMF), hexamethylphosphoramide(HMPA), dimethylacetamide (DMA) or dimethylsulfoxide (DMSO).

Also, the metal ion for the phosphorous-based alloy may use Ni²⁺, Cu²⁺,Ti⁴⁺, Al³⁺, Cr²⁺, Cr³⁺, Cr⁶⁺, Mn²⁺, Mn³⁺, Mn⁴⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺,Zn²⁺, Ga³⁺, Ge⁴⁺, As⁴⁺, Pd²⁺, Ag⁺, In²⁺, In³⁺, Sn²⁺, and W⁶⁺, and is notlimited thereto.

Advantageous Effects

An anode active material of the present disclosure in which aphosphorus-based alloy coating layer is provided on a surface of acarbon-silicon composite having a cavity may relieve stress caused byvolume expansion generated upon alloying of lithium and Si, when used ina lithium secondary battery.

Also, a method of manufacturing the anode active material of the presentdisclosure may ease the thickness control of the phosphorous-based alloycoating layer formed on the surface of the carbon-silicon compositethrough controlling a plating temperature and a plating time, and mayenable recovery of a plating solution.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate a preferred embodiment of thepresent disclosure and together with the foregoing disclosure, serve toprovide further understanding of the technical spirit of the presentdisclosure. However, the present disclosure is not construed as beinglimited to the drawings.

FIG. 1 is a diagram illustrating an apparatus for manufacturing an anodeactive material for a lithium secondary battery according to anexemplary embodiment.

FIG. 2 is a diagram illustrating a process of manufacturing an anodeactive material for a lithium secondary battery according to anexemplary embodiment.

FIG. 3 is a flowchart schematically illustrating a procedure ofEmbodiment example 1.

FIG. 4a is a diagram schematically illustrating a section of thecarbon-silicon composite according an embodiment of the presentinvention and FIG. 4b is a photographic image of an active materialobtained in Embodiment example 1.

FIG. 5 illustrates a volume expansion result of electrodes manufacturedin Embodiment example 1 and Comparative example 1 duringcharge/discharge cycles.

FIG. 6 illustrates a cycle characteristics result of electrodesmanufactured in Embodiment example 1 and Comparative example 1.

BEST MODE FOR EMBODIMENT OF THE INVENTION

Hereinafter, the present disclosure will be described in detail. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

FIG. 1 illustrates an embodiment of an apparatus for manufacturing ananode active material for a lithium secondary battery according to thepresent disclosure. Also, FIG. 2 illustrates an embodiment of a processof manufacturing an anode active material for a lithium secondarybattery according to the present disclosure. However, the descriptionproposed herein is just a preferable example for the purpose ofillustrations only, not intended to limit the scope of the disclosure,so it should be understood that other equivalents and modificationscould be made thereto without departing from the spirit and scope of thedisclosure.

An anode active material for a lithium secondary battery according tothe present disclosure comprises a carbon-silicon composite including acore wherein a cavity is formed therein, and a coating layer formed on asurface of the core and including a phosphorus (P)-based alloy (SeeFIGS. 4a and 4b ).

The anode active material functions to absorb lithium ions in a cathodeactive material during charging and then generates electric energy alongthe concentration gradient of lithium ions during the deintercalation ofthe absorbed lithium ions. If Si having high charging/dischargingcapacity is used as anode active material, Si forms an alloy withlithium ions during the absorption of lithium ions to cause volumeexpansion. To solve the volume expansion problem of Si, the presentdisclosure introduced a coating layer including a phosphorus-based alloyon a surface of a carbon-silicon composite having a cavity formedtherein. The structure of the carbon-silicon composite will be explainedherein below, referring to FIG. 4 a.

The carbon-silicon composite (400) is prepared by carbonizing a siliconpolymer particle in a reducing atmosphere, and includes not only acarbon-silicon bond but also a carbon-silicon oxide bond containingoxygen. The use of the carbon-silicon composite contributes toalleviation of volume expansion of Si.

Also, such a carbon-silicon composite (400) has a cavity (410) insidethe core, and due to this cavity, a surface area of the carbon-siliconcomposite is increased, and when the volume of Si expands, the cavitymay act as a buffer. The cavity is located at the approximate center inthe core of the carbon-silicon composite. Therefore, the center of thecarbon-silicon composite is empty. The cavity occupies from 20 to 80volume % of the carbon-silicon composite. Such cavity relieves thestress generated from the volumetric expansion.

The carbon-silicon composite (400) includes the core (410) having thecavity formed therein and the coating layer which includes thephosphorus (P)-based alloy and covers the core. The phosphorus (P)-basedalloy is an alloy containing phosphorus, and includes alloys ofphosphorus and metals such as Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga,Ge, As, Pd, Ag, In, Sn, and W. The phosphorus-based alloy is coated onthe surface of the carbon-silicon composite to reduce degradation of theactive material caused by the volume expansion.

The coating layer (430) include the layer (431) entirely covering thecore. Further, the coating layer (430) may further include a pluralityof domains (432) protruded from the layer (431) like embossed shape. Thedomains (432) are formed of and filled with the same material as thelayer (431), both of which includes the phosphorus (P)-based alloy, andare continuously connected to the layer (431). Besides, the domains(432) may be formed at a distance from each other and may in totaloccupy from 40 to 60% of surface area of the layer (431). The domains(432) may have a hemisphere shape or a similar shape with thehemisphere. Therefore, the domains (432) may have a circular top-viewand the height (thickness) and/or diameter of each of the domains (432)can be different. In the present disclosure, the word ‘circle’ or‘circular’ means any circle-like or circle-similar shape including ovaland distorted circle. The domains may be formed all over the layercovering the core surface. Also, an average diameter of the domains or athickness of the coating layer including the domains is preferably equalto or less than 0.1 μm, and because the thickness greater than 0.1 μmhinders diffusion of the lithium ion through the domains, theexcessively thick coating layer is not preferred.

Particularly, a density of the phosphorus-based alloy of the presentdisclosure is preferably in a range of 1.2 to 5.8 g cm⁻³.

A specific surface area of the core of the carbon-silicon composite ispreferably equal to or less than 10 m²/g. When the specific surface areaof the core is greater than 10 m²/g, initial efficiency of the anode mayreduce. In the present disclosure, a lower bound of the specific surfacearea of the core is not specially limited. A preferred lower bound maybe 5 m²/g, however this is just an example and is not limited thereto.

Also, the core may have a particle diameter in a range of 0.5 μm to 100μm, preferably, 0.5 μm to 40 μm. When the average particle diameter ofthe core is less than 0.5 μm, initial efficiency of the anode may reducedue to fine powder of the core, and when the average particle diameteris greater than 100 μm, procedural efficiency of the anode slurrycoating may reduce and scratches on an electrode may increase.

The anode active material of the present disclosure may be manufacturedby the following method.

First, silicon polymer particles with the metal catalyst supported onthe surface are prepared by treating silicon polymer particles with ametal chloride solution.

The silicon polymer represents a polymer containing at least one heteroatom such as silicon (Si) within a polymer repeat unit. The siliconpolymer used in the present disclosure is not limited to a specifictype, but may use particles of silicone resin, for example,polysiloxane, polysilane, and polycarbosilane. More preferably, anemulsion type in which silicon polymer particles in latex form areuniformly dispersed in a dispersion medium may be used.

Also, the metal chloride solution may be one that metal chlorideselected from PdCl₂, SnCl₂, and CuCl₂ is dissolved in an aqueoussolution of nitrohydrochloric acid or hydrochloric acid, or in a polarorganic solvent of dimethylformamide (DMF), hexamethylphosphoramide(HMPA), dimethylacetamide (DMA) or dimethylsulfoxide (DMSO).

The silicon polymer particles are treated with the metal chloridesolution, so that a metal from metal chloride is supported on thesurface of the silicon polymer particles. The metal may act as acatalyst in a subsequent reaction process.

Subsequently, the silicon polymer particles with the catalyst supportedon the surface are dispersed in a plating bath filled with a platingsolution containing a metal ion for a phosphorus-based alloy andphosphoric acid.

Referring to FIG. 1, the plating bath has a stirrer at the bottomthereof to uniformly disperse, in the plating solution, the siliconpolymer particles with the catalyst supported on the surface. As theplating solution, various types of plating solutions may be used, and adetailed description is as follows. In the case of an acidic electrolessnickel plating solution, a mixture of a phosphorus-based alloy metal ionand sodium hypophosphite (NaH₂PO₂.H₂O) in an aqueous solution of lacticacid, propionic acid (CH₃CH₂COOH), sodium acetate (CH₃CO₂Na), sodiumsuccinate (CH₃CH₂COOH), malic acid or sodium citrate may be used, and inthe case of an alkaline electroless nickel plating solution, a mixtureof a phosphorus-based alloy metal ion and sodium hypophosphite(NaH₂PO₂.H₂O) in an aqueous solution of ammonium chloride (NH₄Cl) orsodium pyrophosphate may be used.

As the metal ion used in the phosphorus-based alloy metal ion, Ni²⁺,Cu²⁺, Ti⁴⁺, Al³⁺, Cr²⁺, Cr³⁺, Cr⁶⁺, Mn²⁺, Mn³⁺, Mn⁴⁺, Fe²⁺, Fe³⁺, Co²⁺,Co³⁺, Zn²⁺, Ga³⁺, Ge⁴⁺, As⁴⁺, Pd²⁺, Ag⁺, In²⁺, In³⁺, Sn²⁺, and W⁶⁺ maybe used, singularly or in combination.

Subsequently, the bath is heated to form phosphorus (P)-based alloysurface-coated silicon polymer particles.

The plating bath of FIG. 1 may use a hot plate to perform heating.Heating is performed while stirring the plating solution favorably byoperating the stirrer. In this instance, a preferred temperature is in arange of 40 to 100° C. Through heating, phosphoric acid reacts with thephosphorus-based alloy ion, in the presence of the catalyst, on thesurface of the silicon polymer particles to form phosphorus-based alloysurface-coated silicon polymer particles. Preferably, thephosphorus-based alloy may be coated while forming domains.

Finally, the phosphorus (P)-based alloy surface-coated silicon polymerparticles are carbonized by heat treatment in a reducing atmosphere.

The reducing atmosphere is not particularly limited, but a reducingatmosphere such as H₂ or N₂ may be used. By carbonizing thephosphorus-based alloy surface-coated silicon polymer particles throughheat treatment in a range of about 800 to 1200° C., oxygen or hydrogeninside is discharged outwards to form a cavity. In such a way, the anodeactive material of the present disclosure in which the phosphorus-basedalloy coating layer is provided on the surface of the carbon-siliconcomposite having the cavity may be manufactured.

In FIG. 2, a process of forming the phosphorus-based alloy on thesurface of the silicon polymer particles with the metal catalystsupported on the surface and a process of forming the anode activematerial having the cavity formed therein by heat treatment areillustrated. The phosphorus-based alloy may be easily formed due to themetal catalyst supported on the surface of the silicon polymerparticles, and the internal cavity may be formed by high heat treatmentin the reducing atmosphere.

The anode active material of the present disclosure manufactured asdescribed in the foregoing may be used to manufacture an anode by amanufacturing method generally used in the art. Also, a cathodeaccording to the present disclosure may be manufactured by a methodgenerally used in the art. For example, the electrode may bemanufactured by mixing an electrode active material of the presentdisclosure with a binder, a solvent, if necessary, a conductive materialand a dispersant, agitating the mixture to prepare a slurry, applyingthe slurry to a current collector, and compressing the result.

As the binder, various types of binder polymers may be used, forexample, polyimide, polyvinylidene fluoride-co-hexafluoro propylene(PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile,polymethylmethacrylate, and the like. In case that polyimide is used asbinder for the anode active material, performance deterioration ofbattery which is resulted from the contraction-expansion ofcarbon-silicon during the battery use can be inhibited since polyimidecan physically strongly bind the carbon-silicon composite.

As the cathode active material, lithium-containing transition metaloxide may be preferably used, for example, any one selected from thegroup consisting of Li_(x)CoO₂(0.5<x<1.3), Li_(x)NiO₂(0.5<x<1.3),Li_(x)MnO₂(0.5<x<1.3), Li_(x)Mn₂O₄(0.5<x<1.3),Li_(x)(Ni_(a)Co_(b)Mn_(c))O₂(0.5<x<1.3, 0<a<1, 0<b<1, 0<c<1, a+b+c=1),Li_(x)Ni_(1-y)Co_(y)O₂(0.5<x<1.3, 0<y<1),Li_(x)Co_(1-y)Mn_(y)O₂(0.5<x<1.3, 0≦y<1),Li_(x)Ni_(1-y)Mn_(y)O₂(0.5<x<1.3, O≦y<1),Li_(x)(Ni_(a)Co_(b)Mn_(c))O₄(0.5<x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2),Li_(x)Mn_(2-z)Ni_(z)O₄(0.5<x<1.3, 0<z<2),Li_(x)Mn_(2-z)Co_(z)O₄(0.5<x<1.3, 0<z<2), Li_(x)CoPO₄(0.5<x<1.3) andLi_(x)FePO₄(0.5<x<1.3) or mixtures thereof, and the lithium-containingtransition metal oxide may be coated with a metal such as aluminum (Al)or metal oxide. Also, besides the lithium-containing transition metaloxide, sulfide, selenide, and halide may be used.

When the electrode is manufactured, a lithium secondary batterygenerally used in the art, in which a separator interposed between thecathode and the anode and an electrolyte solution are included, may bemanufactured using the electrode.

In the electrolyte solution used in the present disclosure, a lithiumsalt included as an electrolyte may use, without limitation, thosegenerally used in an electrolyte solution for a lithium secondarybattery, and for example, an anion of the lithium salt may be any oneselected from the group consisting of F⁻, Cl⁻, Br⁻, I⁻, NO₃ ⁻, N(CN)₂ ⁻,BF₄ ⁻, ClO₄ ⁻, PF₆ ⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻,(CF₃)₆P⁻, CF₃SO₃ ⁻, CF₃CF₂SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻,CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (CF₃SO₂)₃C⁻, CF₃(CF₂)₇SO₃ ⁻,CF₃CO₂ ⁻, CH₃CO₂ ⁻, SCN⁻, and (CF₃CF₂SO₂)₂N⁻.

In the electrolyte solution used in the present disclosure, an organicsolvent included in the electrolyte solution may include, withoutlimitation, those generally used in an electrolyte solution for alithium secondary battery, as a representative example, any one selectedfrom the group consisting of propylene carbonate (PC), ethylenecarbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC),ethylmethylcarbonate (EMC), methylpropyl carbonate, dipropyl carbonate,dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane,vinylene carbonate, sulfolane, gamma butyrolactone, propylene sulfateand tetrahydrofuran, or mixtures thereof. Particularly, among thecarbonate-based organic solvents, cyclic carbonate such as ethylenecarbonate and propylene carbonate corresponds to an organic solventhaving a high viscosity, and is preferred to use because it dissociatesa lithium salt in an electrolyte favorably due to its high dielectricconstant, and in this instance, such cyclic carbonate is more preferredto use because it contributes to form an electrolyte solution havinghigh electrical conductivity when mixed with linear carbonate having alow viscosity and a low dielectric constant such as dimethyl carbonateand diethyl carbonate at a proper ratio.

Optionally, the electrolyte solution stored according to the presentdisclosure may further include an additive, such as an overchargeinhibitor, used in a general electrolyte solution.

Also, as the separator, a general porous polymer film employed as aseparator in the art may be used, for example, a porous polymer filmmade from a polyolefin-based polymer such as an ethylene homopolymer, apropylene homopolymer, an ethylene/butene copolymer, an ethylene/hexenecopolymer, and an ethylene/methacrylate copolymer, arranged singularlyor in a stack, or a general porous non-woven fabric, for example, anon-woven fabric made from a glass fiber having a high melting point, apolyethyleneterephthalate fiber, and the like, however the presentdisclosure is not limited thereto.

A battery casing used in the present disclosure may employ thosegenerally used in the art, and is not limited to a specific outer shapebased on usage of the battery, and the battery casing may have, forexample, a cylindrical shape using a can, a prismatic shape, a pouchshape, a coin shape, and the like.

MODE FOR EMBODIMENT OF THE INVENTION

Hereinafter, a detailed description is provided through an embodimentexample and a comparative example to describe embodiments and effects ofthe present disclosure more specifically. However, it should beunderstood that embodiments of the present disclosure may be modified invarious forms and the scope of the invention is not limited to thefollowing embodiment. The embodiments of the present disclosure areprovided to describe the present disclosure to those skilled in the artmore completely.

EMBODIMENT EXAMPLE Embodiment Example 1 Manufacture of an Anode ActiveMaterial with an Electroless Plating Layer and a Battery Comprising theSame

An electroless plating layer on silicon polymer was manufactured inaccordance with the flowchart of FIG. 3.

5 ml of a suspension solution containing 48 wt % of solids includingpolycarbosilane was put in 100 ml of an aqueous catalyst solutioncontaining 0.1 g of PdCl₂ and 50 μl of nitrohydrochloric acid, followedby impregnation at about 5° C. for 24 hours, so that the Pd catalyst wasadsorbed on the surface of the silicon polymer particles, and suctionfiltration and washing was conducted on the catalyst-adsorbed solutionto collect powder in cake form. The collected powder was put in anelectroless NiP plating solution including 15 g/L of Ni(PH₂O₂)₂.6H₂O,12.0 g/L of H₃BO₃, 2.5 g/L of CH₃COONa, and 1.3 g/L of (NH₃)₂SO₄, andafter reaction at 30° C. for about 5 minutes, a precipitation reactionof Ni was stopped by lowering the temperature with ice water.Subsequently, the resulting NiP-plated silicon polymer was collectedthrough suction filtration, and freeze-dried to completely remove water.

Powder obtained through freeze-drying was heat-treated at temperature of1000° C. in an inert atmosphere of N₂ or Ar or a reducing atmosphere inwhich H₂ is present in part. In this instance, through reduction andcarbonization of the silicon polymer, a silicon-carbon composite wasformed.

In FIG. 4, a photographic image of an active material obtained throughelectroless plating and heat treatment of a silicon polymer particulateis shown. As seen in FIG. 4, a spheric particle having a diameter ofabout 0.6 μm was obtained.

An NMP (N-methyl pyrrolidone)-based organic slurry was prepared based ona composition including the active material, VGCF as a conductivematerial, and a polyimide-based binder as a binder at 95:1:4, and wasapplied to a Cu current collector, followed by drying and pressingprocesses, to manufacture an electrode. A coin cell was manufacturedusing the manufactured electrode, a metal lithium as an oppositeelectrode, and an EC+EMC organic solvent containing 1M LiPF₆ as anelectrolyte.

Comparative Example 1 Manufacture of an Anode Active Material without anElectroless Plating Layer and a Battery Comprising the Same

An anode active material and a coin cell were manufactured by the samemethod as Embodiment example 1 except an electroless plating layer wasnot formed on silicon polymer.

EVALUATION EXPERIMENT

In FIG. 5, an average of volume expansion of an electrode during three(3) charge/discharge cycles is shown. To show the extent of volumeexpansion of the electrode, a thickness of the electrode at charge oneach cycle was measured relative to an initial thickness of theelectrode. The electrode of Embodiment example 1 using the activematerial with NiP electroless plating and heat treatment exhibited lessvolume expansion on each cycle than the electrode of Comparative example1 using the active material without electroless plate coating, and thus,was found to be effective in suppressing the volume expansion.

In FIG. 6, the cycle characteristics result of the electrodesmanufactured in Embodiment example 1 and Comparative example 1 areshown. It was found that the electrode of Comparative example 1 withoutplating exhibited the deterioration in cycle characteristics during 10cycles, while the NiP-plated electrode of Embodiment example 1suppressed an extent of cycle characteristic deterioration.

What is claimed is:
 1. An anode active material for a lithium secondarybattery, comprising. a core including a carbon-silicon composite andhaving a cavity formed inside; and a coating layer formed on a surfaceof the core and including a phosphorus (P)-based alloy wherein thecoating layer entirely covers the surface of the core wherein thecarbon-silicon composite comprises carbon-silicon bonds.
 2. The anodeactive material for the lithium secondary battery according to claim 1,wherein the coating layer has a plurality of domains which are protrudedfrom the coating layer surface.
 3. The anode active material for thelithium secondary battery according to claim 1, wherein thephosphorus-based alloy is an alloy of phosphorous and a metal selectedfrom the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge,As, Pd, Ag, In, Sn, and W.
 4. The anode active material for the lithiumsecondary battery according to claim 1, wherein the carbon-siliconcomposite further includes oxygen.
 5. The anode active material for thelithium secondary battery according to claim 1, wherein a density of thecoating layer is in a range of 1.2 to 5.8 g cm⁻³, and a thickness of thecoating layer including the domains is equal to or less than 0.1 μm. 6.The anode active material for the lithium secondary battery according toclaim 1, wherein a specific surface area of the core is equal to or lessthan 50 m²/g.
 7. The anode active material for the lithium secondarybattery according to claim 1, wherein an average particle diameter ofthe core is in a range of 0.5 to 100 μm.
 8. An anode for a lithiumsecondary battery, the anode comprising: a current collector; and ananode active material layer formed on at least one surface of thecurrent collector and including an anode active material and binder,wherein the anode active material is an anode active material defined inclaim
 1. 9. An anode for a lithium secondary battery according to claim8, wherein the binder is polyimide.
 10. A lithium secondary batterycomprising: a cathode; an anode; and a separator interposed between thecathode and the anode, wherein the anode is an anode defined in claim 8.